For example, as the technologies in the field of a system LSI for performing a large amount of data transfer among a plurality of circuit modules, the inventors of the present invention have examined the following technologies.
In a SOC (System On a Chip) in which a number of circuit modules are incorporated, the circuit modules which have not had strong connection with each other are directly connected to one another by an on-chip bus in the LSI. In such a LSI, the control of resource conflict among a plurality of circuit modules is an important factor for determining the system performance.
Hereinafter, the circuit module which outputs a resource use request to other circuit module will be referred to as “master”, and the resource which is to be used on the other hand will be referred to as a “target resource”.
In recent years, the problem of the resource conflict has drawn attention. Particularly, in the field of built-in microcomputers, the demand for performing a large amount of real-time data processing, for example, the high-resolution video processing has been increasing. In such real-time applications, a control method for compensating the amount of target resource usage for each of the tasks executed on a master is required. In actual use, it is important to have tolerance against variation in the timing of target resource use requests for each task and to have flexibility which enables optimization according to the usage of the user.
The variation in timing mentioned here means that the timing of target resource requests outputted from the masters is not constant. If the target resource use requests are always being outputted or always have a limited pattern, it is easy to compensate the target resource usage amounts for the masters. However, in practice, the requests are affected by the types of the applications, access timing from outside the LSI and the like and are changed in a complicated manner. Even when such changes occur, the target resource usage amounts for the masters have to be compensated.
The method used most commonly is a round-robin method which is also used in Japanese Patent Application Laid-Open Publication No. 2002-269032. This is a method in which the right to use a target resource is given to conflicting masters in a predetermined order. This is a simple method and has a merit in terms of circuit implementation since the circuit scale is small. However, since the order of using the target resource is fixedly allocated, if a master cannot issue a target resource use request at the timing when the usage order of the master is allocated, the master cannot use a planned amount of the target resource, which affects the performance. As described above, the target resource usage amount cannot be compensated for each of the masters in some cases when the process request timing of the master is varied.
Also, as a method frequently used in a real-time compensation system, a method in which the right to occupy a target resource is fixedly given in a time-sharing manner is known. In this method, the target resource usage amounts can be precisely compensated for connected masters. However, when the master cannot output a request in the cycle in which it is prioritized due to the above-described variation, the target resource is not effectively utilized, and a wasted cycle is caused.
A method for effectively utilizing the wasted cycle is the method disclosed in Japanese Patent Application Laid-Open Publication No. 2004-5677. In this method, when there is no request from the most prioritized master, a request from another master is accepted so as to effectively utilize the target resource. However, even in this method, when the above-described variation occurs, the target resource usage amount for each of the tasks cannot be compensated in some cases.
In addition, in relation to the point of flexibility, for example, as disclosed in Japanese Patent Application Laid-Open Publication No. 9-185580, a method in which the flexibility is realized by providing a rewritable storage device in the interior is known.